System and method for determining a position of an object

ABSTRACT

A system is disclosed for determining a position and a change in the position of an anatomical structure. The system utilizes a surgical navigation system and a substrate that is capable of being removably mounted to an outer surface of a patient&#39;s body. The substrate includes a sensor that is tracked by the surgical navigation system and a positional device that determines the position of an anatomical structure relative to the sensor. The concatenation of the position of the sensor and the relative position of the anatomical structure allows a global position of the anatomical structure to be determined by a computer system and displayed to the user.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/644,285, filed Dec. 22, 2009, which is a divisional of U.S. patentapplication Ser. No. 10/798,614, filed Mar. 11, 2004, the entirety ofwhich is hereby incorporated by reference herein.

REFERENCE REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

SEQUENTIAL LISTING

Not applicable

BACKGROUND

1. Technical Field

This invention relates generally to surgical navigation systems. Moreparticularly, this invention relates to a positional device attached toa substrate that assists in determining the position and relativemovement of an anatomical structure within a patient.

2. Background Art

The use of surgical navigation systems for assisting surgeons duringsurgery is quite common. Some systems are used to track the movement ofbony structures. Determining the precise location of a bony structure,and whether it has moved, is essential when utilizing surgicalinstruments in fields such as orthopedic surgery. Typical surgicalnavigation systems utilize trackers that are rigidly attached to theunderlying bony structure being monitored. Rigid attachment ofnavigation trackers to the bony structure is often an extremely invasiveprocedure that may cause additional trauma to the patient and wastes asignificant amount of time. The present invention provides a system formonitoring the position and change in position of a bony structure withlittle or no invasiveness in a shorter amount of time.

SUMMARY OF THE INVENTION

One embodiment of the present invention is directed to a system fordetermining a position and a change in the position of an anatomicalstructure. The system includes a surgical navigation system and asubstrate including means for removably attaching the substrate to anouter surface of a body, wherein the body includes an anatomicalstructure. A sensor is attached to the substrate that can be tracked bythe surgical navigation system to determine a position of the sensor andan ultrasonic imaging device is attached to the substrate and can beutilized to determine a position of the anatomical structure relative tothe sensor. The system further includes a first circuit for calculatinga global position of the anatomical structure by concatenating theposition of the sensor and the position of the anatomical structurerelative to the sensor and a second circuit for displaying the globalposition of the anatomical structure on a display unit.

Another embodiment of the present invention is directed to a method fordetermining a position and a change in the position of an anatomicalstructure spaced interiorly from an outer surface of a body using asurgical navigation system and a substrate. The substrate includes meansfor non-invasive attachment to the outer surface of the body, a sensorconnected with the substrate, and a positional device for determining aposition of the anatomical structure relative to the sensor wherein thepositional device includes an ultrasonic imaging device attached to thesubstrate. The method includes the steps of attaching the substrate in aremovable manner to an outer surface of the body with the means forattachment and determining a position of the anatomical structurerelative to the sensor using the ultrasonic imaging device. The methodalso includes the step of tracking the sensor with the surgicalnavigation system to determine a position of the sensor. The methodfurther includes the steps of determining the global position of theanatomical structure by concatenating the position of the sensor and theposition of the anatomical structure relative to the sensor, anddisplaying the position of the anatomical structure on a display unit.

Other aspects and advantages of the present invention will becomeapparent upon consideration of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an embodiment of the system of the presentinvention;

FIG. 2 is top plan view of one embodiment of a substrate with apositional device;

FIG. 3 is a top plan view of an embodiment similar to the one seen inFIG. 2 with an ultrasonic imaging device;

FIG. 4 is an isometric view of a further embodiment of the presentinvention utilizing an ultrasonic imaging device;

FIG. 5 is an isometric view of another embodiment of the presentinvention utilizing an ultrasonic imaging device;

FIG. 6 a is another isometric view of the embodiment in FIG. 4 with aremoval device shown;

FIG. 6 b is another isometric view of the embodiment in FIG. 5 with aremoval device shown;

FIG. 7 is an isometric view of a still further embodiment of the presentinvention utilizing a magnetic tracker;

FIG. 8 is an isometric view of yet another embodiment of the presentinvention utilizing a magnetic tracker;

FIG. 9 is a side elevational view of an impaction device suitable foruse in an embodiment of the present invention;

FIG. 10 is an isometric view of an additional embodiment of the presentinvention utilizing a fiber optic device;

FIG. 11 is a cross section of a fiber suitable for use in the device ofFIG. 10;

FIG. 12 is a cross section of a fiber similar to FIG. 11;

FIG. 13 is a cross section of a fiber showing axes of sensitivity for abend sensor;

FIG. 14 is an embodiment of the fiber optic device that shows how lightis transmitted between fibers;

FIG. 15 is a perspective view of three fibers with bending sensorsdisposed on different areas of each respective fiber; and

FIG. 16 is a further embodiment of a fiber optic device using a seriesof looped sensors.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

With reference to FIG. 1, the present invention is directed toward asystem 100 for determining a position and a change in the position of ananatomical structure 102. The system 100 includes a navigation system(also known as a “surgical navigation system”) 104 and a substrate 106.The substrate 106 includes a sensor 108 for interacting with thenavigation system 104 and a positional device 110 for determining theposition of the anatomical structure 102. The substrate 106 is removablymounted to an outer surface 111 of a body 112. In a preferred embodimentof the present invention, the anatomical structure 102 found in the body112 is a bony structure 114. However, the anatomical structure 102 mayalso be any organ or other structure found within the body 112 of thepatient. As such, any of the embodiments hereinafter mentioned inrespect to the bony structure 112 may also be used with organs or otherstructures that may comprise the anatomical structure 102.

The surgical navigation system 104 includes a computer system 140 and acamera array 142. The computer system 140 may be housed in a moveablecart 144. The computer system 140 may be any type of personal computerhaving a memory unit, a CPU, and a storage unit. A display unit 152 mayalso be provided, which can be any conventional display usable with apersonal computer.

The camera array 142 is adapted to track the sensor 108. The cameraarray 142 is further adapted to transmit data between the sensor 108 andthe computer system 140 representing the position of the sensor 108. Ina preferred embodiment, the data is transmitted wirelessly between thesensor 108 and the computer system 140. Alternatively, a system thatuses wires to transmit data between the sensor 108 and the computersystem 140 can be used.

The positional device 110 is adapted to track the bony structure 114.Data from the positional device 110 represents the position of the bonystructure 114 in relation to the position of the sensor 108. In apreferred embodiment, the positional device 110 is further adapted totransmit the data directly to the computer system 140. Preferably, thesystem will transmit the data wirelessly; however, transmission by wirescan also be accomplished. In other embodiments, the data from thepositional device 110 may be first communicated to the sensor 108 orcamera array 142, prior to the data being sent to the computer system140.

The camera array 142 includes a first camera 154, a second camera 156,and a third camera 158. In a preferred embodiment, the first, second andthird cameras, 154, 156, and 158, are three CCD cameras adapted todetect the position of infrared signals (IR) generated by the sensor108. In such an embodiment, the sensor 108 is an optical tracking devicethat comprises a plurality of LED's 159. In a preferred embodiment, theoptical tracking device includes three LED's.

The camera array 142 should be mounted in a stationary position with asufficient line of sight to the operating room. In one embodiment, thecamera array 142 is mounted on a rotatable arm 160 attached to a movablestand or cart 144. In another embodiment, the camera array 142 may bemounted onto an operating room wall (not shown) or onto other convenientsurfaces or locations.

At least one infrared transceiver is used to communicate data to andfrom the sensor 108 and/or positional device 110. In the preferredembodiment, the camera array 142 includes a first transceiver 162 and asecond transceiver 164 located apart from each other. It should be notedthat while both the sensor 108 and/or positional device 110 maycommunicate with the transceivers 162, 164 via infrared signals, thoseskilled in the art will realize other wireless technologies, such asthose that utilize electromagnetic signals (e.g. radio frequency), maybe used as well as hardwired systems. Similarly, direct communicationfrom the positional device 110 to the computer system 140 may utilizeany of these communication mediums. The camera array 142 is connectedvia a cable 166 to a localizer or in some instances directly to thecomputer system 140. The localizer cooperates with the camera array 142to identify the location of the plurality of LED's 159 included in thesensor 108 within the line of sight of the camera array 142. In oneembodiment, the localizer converts the raw position data into theposition of individual LED's of the plurality of LED's 159 and transmitsthis information to the computer system 140. In another embodiment, thelocalizer converts the raw data into the position of the sensor 108 andtransmits this information to the computer system 140.

The overall tracking of the bony structures 114 is achieved throughconcatenation of the positional data from the sensor 108 and thepositional device 110. A software program in the computer system 140 canconvert the raw positional data from both the sensor 108 and thepositional device 110 to determine the global position of the bonystructures 114. In all embodiments, the conversion of the raw data iswell known to one skilled in the art and need not be further discussed.

Preferably, the substrate 106 is capable of being removably mounted tothe outer surface 111 of the body 112. The substrate of FIG. 2 includesa first side 180 and a second side 182. In a preferred embodiment, thepositional device 110 is disposed on the first side 180 of the substrate106 and the sensor 108 is disposed on the second side 182 of thesubstrate 106. It is also envisioned that the positional device 110 andthe sensor 108 may be situated on the same side or disposed in any of avariety of positions so long as the sensor 108 can communicate with thecamera array 142 and the positional device 110 can track the position ofthe underlying anatomical or bony structures 102, 114. Typically, thesensor 108 and the positional device 110 are in a fixed relation. Insituations where the sensor 108 and the positional device 110 are not ina fixed relation, the relationship between the two may be deduced byknown methods. The substrate 106 may also take on a variety of formsdependent on the user's needs and/or the type of positional device 110used. In one embodiment, the substrate 106 is made of a flexiblematerial that will not interfere with ultrasound waves. In anotherembodiment, the substrate 106 is formed from polyester and similarmaterials that will not interfere with magnetic fields. In oneparticular embodiment, the substrate is about 5 cm in length and about 5cm in width. The substrate 106 may be mounted to the outer surface 111of the body 112 by an adhesive material, a band, or any other suitableattachment means presently used in conventional surgical operations.

As shown in FIG. 3, the positional device 110 is an ultrasonic imagingdevice 200. Ultrasonic imaging devices 200, such as those used in U.S.Pat. No. 6,390,982 and U.S. Pat. No. 6,338,716 that are hereinafterincorporated by reference, are well known in the art. The ultrasonicimaging device 200 is disposed on the first side 180 of the substrate106 while the sensor 108 is attached to the second side 182 of thesubstrate 106. By concatenating the positional data from the ultrasonicimaging device 200 and the positional data from the sensor 108, theglobal position and global change in position of the bony structures 114may be calculated and displayed. The present embodiment has the addedadvantage of allowing the global position of the bony structure 114 tobe determined without having a priori knowledge of the bony structure114. Therefore, in one embodiment an image of the bony structure 114 isnot needed to determine the global position. If used, the image could bea pre-operative image, an intra-operative image, or any other imagetypically used in surgical procedures.

The ultrasonic imaging device 200 allows the user to track the positionof an underlying bony structure 114 without the need to invasively fix atracking device to the body 112. The ultrasonic imaging device 200comprises at least three ultrasound transducers 220. The ultrasoundtransducers 220 are made up of several piezoelectric elements that maybe arranged separately or combined as desired. Multiple piezoelectricelements are sometimes arranged in patterns in a common housing, theseare usually linear, matrix or annular in shape. The elements may bepulsed simultaneously, or the elements may be pulsed in a certainpattern to each other.

In the present embodiment, the ultrasound transducers 220 are disposedon the first side 180 of the substrate 106. The plurality of LED's 159included in the sensor 108 are disposed on the second side 182 of thesubstrate 106. Positional data garnered from the ultrasound transducers220 relates the position of the underlying bony structure 114 to thesensor 108. The knowledge of the relationship between the sensor 108 andthe ultrasound transducers 220 will typically be known, but may bededuced from the shape described by the sensor 108 if the relationshipis unknown or non-constant. The computer system 140 calculates theglobal position of the bony structure 114 by concatenating the positionof the sensor 104 and the relative position of the bony structure 114 tothe sensor 108.

In one embodiment, the ultrasonic imaging device 200 is initialized byfirst mapping a sub-area of the bony structure 114 covered by thedevice. It may be necessary to apply a slight motion to the ultrasonicimaging device 200 to create differential distance maps of the bonystructure 114 in order to discard discrepancies. By considering numerousdistance maps of the static and moving ultrasonic imaging device 200,the data can be correlated so that an arbitrary initial distance map canbe established. Further, this embodiment will also establish anarbitrary transformation between the bony structure 114 coordinates andthe sensor 108 so as to establish a position of the bony structure 114in relation to the sensor 108. As mentioned before, the positional datafrom the bony structure 114 and the sensor 108 will then be concatenatedto determine the global position of the bony structure 114.

By constantly mapping the bony structure 114 and comparing the data withthe arbitrary initial position, the relative movement of the bonystructure 114 can be determined and relayed to the user. The distancemap produced may be a three dimensional or two dimensional distance map.In either scenario, the navigational system 104 or ultrasonic imagingdevice 200 will still track the underlying bony structure 114 andcorrelate this information with the initial bony structures 114 positionto determine if the position of the bony structure 114 has changedand/or to supplement the initial position data. Additionally, as morepositional data of the bony structure 114 is accumulated, the initialdistance map will grow to include missing data.

In order to increase tracking accuracy, some embodiments utilizemultiple ultrasonic imaging devices 200 and sensors 108 to track thebony structure 114. Such coupled trackers can be distributed radially oraxially over larger areas of the outer surface of the patient to coverdistant portions of the same bony structure 114. By utilizing multiplecoupled trackers, and taking into consideration the relative position ofthe coupled trackers to each other, the captured information per unitcan be decreased without loss of accuracy. The coupled trackers may becalibrated by temporarily introducing a known calibration object (notshown) into the surrounding tissue of the patient's body. In someembodiments, the calibration object is disposed within the tissue of thepatient at a known distance from the coupled trackers. In instanceswhere the calibration object is disposed an unknown distance from thecoupled trackers, the calibration object can be used to determine therelative distances between the coupled trackers. In one embodiment, thecalibration object is a thin translucent needle with an ultrasonic tip.

The ultrasonic imaging device 200 of the last embodiment may be utilizedalong with passive point sources to aid in the positioning of the bonystructure 114. At least three passive point sources must be used. It isalso envisioned that multiple ultrasonic imaging devices 200 may be usedin a similar manner as discussed above, including the calibrationtechniques expounded upon. In the embodiment depicted in FIG. 4, foursonic reflective balls (passive point sources) 240 a, 240 b, 240 c, 240d are percutaneously injected under the transducers 242 a, 242 b, 242 c,242 d and disposed adjacent the bony structure 114. Because the sonicreflective balls 240 a-d lie adjacent the bony structure 114, thedetermination of the position of the sonic reflective balls 240 a-d willindicate the position of the bony structure 114. The transducers 242 a-dare equivalent to the transducers 220 discussed above. The sonicreflective balls 240 a-d may be substantially comprised of air orcomprised of other low density or high density materials. Sonicreflective balls 240 a-d made of high density materials could utilizematerials such as gold and platinum that have good reflectiveproperties. Sonic reflective balls 240 a-d made of low density materialsmay be formed from resorbable materials. Sonic reflective balls 240 a-dcomposed of resorbable material will allow the balls to be absorbedwithin the patient after the procedure has been completed. In oneembodiment, the sonic reflective balls 240 a-d comprise a thin outershell formed of resorbable material with an inner core substantiallycomprised of air. Those skilled in the art will know what materials maybe considered resorbable within the context of the present embodiments.

The position of the sonic reflective balls 240 a-d relative to thesensor 108 is determined by the transducers 242 a-d. As noted before,there is a known relationship between the transducers 242 a-d and thesensor 108. During the positioning process, one transducer is activatedat a time. While any of the transducers 242 a-d can send out the initialultrasonic pulse, for illustrative purposes transducer 242 a has beenmarked as a sending transducer. The sending transducer 242 a emits anultrasonic pulse toward the bony structure 114, which is reflected offof the sonic reflective ball 240 a. All of the transducers 242 a-dreceive the sound wave reflected from the sonic reflective ball 240 a.The length of the path from the sending transducer 242 a to the sonicreflective ball 240 a to the receiving transducers 242 a-d is a functionof the time between when the ultrasound pulse was first emitted and thenlater received by each of the receiving transducers 242 a-d. All of thesonic reflective balls 240 a-d positions can be determined by activatingthe respective transducer 242 a-d above the sonic reflective balls 240a-d one at a time. Those skilled in the art will know how to determinethe position of the bony structure 114 in relation to the sensor 108from the data provided by the transducers 242 a-d and the known distancebetween the transducers 242 a-d and the sensor 108.

FIG. 5 shows the ultrasonic imaging device 200 of the embodiment of FIG.4 modified to utilize active point ultrasonic sources as opposed topassive point sources. At least three active point transducers must beinserted into the tissue under three respective receivers. Similar tothe prior embodiments, multiple ultrasonic imaging devices 200 andcorresponding calibration techniques may be utilized. In the presentembodiment illustrated in FIG. 5, four active point ultrasonictransducers 260 a, 260 b, 260 c, 260 d are disposed adjacent the bonystructure 114 in a similar manner as the sonic reflective balls 240 a-din the last embodiment. Additionally, four receivers 262 a, 262 b, 262c, 262 d are disposed on the first side 180 of the substrate 106,wherein the transducers 262 a-d are in a known relationship with thesensor 108.

Similar to the prior embodiment, the position of active point ultrasonictransducers 260 a-d relative to the sensor 108 is determined by thereceivers 262 a-d. During the positioning process, one of the activesource ultrasonic transducers 260 a-d is activated at a time. Toillustrate the present embodiment, active source ultrasonic transducer260 a has been labeled a sending active source transducer. The sendingactive source ultrasonic transducer 260 a emits an ultrasonic pulse inall directions, which is received by all of the receivers 262 a-d. Basedon the time between the emission of the ultrasonic pulse from thesending active source transducer 262 a and the time the pulse wasreceived by each respective receiver 262 a-d, the length of the pathbetween the sending active source transducer 262 a and each respectivereceiver 262 a-d can be determined. Those skilled in the art will knowhow to determine the position of the bony structure 114 in relation tothe sensor 108 from the data provided by the receivers 262 a-d and theknown distance between the transducers 262 a-d and the sensor 108.

With respect to all the embodiments mentioned above, it is envisionedthat some embodiments may use a single substrate 106 while others willuse multiple substrates 106. As long as at least one transducer 220,transducer 242 a-d, or receiver 262 a-d is included within theultrasonic imaging device 200 on each substrate 106, those skilled inthe art will know how to translate the positional data for eachrespective substrate 106 into a global position of the bony structure114. The substrates 106 used in the present embodiments could beattached by an ultrasonic coupling adhesive known to those in the art tothe outer surface 111 of the body 112. Additionally, the generallyflexible nature of the substrate 106 will not pose a problem, as therelationship of the transducers 220, transducers 242 a-d, and receivers262 a-d to each other and the bony structure 114 need not be fixed atall times. In some embodiments, measurements are taken every 10milliseconds, obviating the need for a more rigid structure for thesubstrate 106. Also, the above embodiments have been described usingfour ultrasound transducers and four ultrasound receivers. It is alsopossible to use three ultrasound transducers and/or receivers andachieve similar results.

The advantages of utilizing an ultrasonic imaging device 200 are easilyseen in patient comfort and user convenience. There is no need for thesurgeon to make further incisions on the patient's body 112 toaccommodate the ultrasonic imaging device 200 or further traumatize theregion undergoing surgery. While a completely non-intrusive embodimenthas been disclosed, even the other embodiments utilizing active andpassive point sources are relatively non-invasive. Nothing needs to bescrewed into the bony structure 114, as the sonic reflective balls 240a-d and the active source transducers 260 a-d are merely disposedadjacent the bony structure 114. Additionally, as may be seen in FIGS. 6a and 6 b, the sonic reflective balls 240 a-d and the active sourcetransducers 260 a-d, respectively, may have a removal device 280attached to them. The removal device 280 may be a wire or any otheranalogous removal mechanism that allows for convenient removal of thesonic reflective balls 240 a-d and active source transducers 260 a-dfrom the body 112 of the patient. The relatively non-invasiveembodiments of the present invention will allow the patient to healfaster and reduce the chance of infection or other complications from amore invasive procedure.

FIG. 7 shows another embodiment of the present invention, wherein thepositional device 110 is a magnetic tracker 300. Magnetic trackingdevices and localization systems such as those taught in U.S. Pat. No.6,073,043, which is hereinafter incorporated by reference, have beenused with limited success in the past. The present embodiment disposesthe magnetic tracker 300 on the first side 180 of the substrate 106while disposing the sensor 108 on the second side 182 of the substrate106. Similar combinations and orientations of the removably mountedsubstrates 108 as discussed above may be used. It is also envisionedthat any of the embodiments related to the sensor 108 and the surgicalnavigation system 104 discussed above may be used in the presentembodiment.

The magnetic tracker 300 of the present embodiment comprises a magnetictransmitter 310 and a magnetic sensor 312. The magnetic transmitter 310is disposed on the substrate 106, while the magnetic sensor 312 isdisposed beneath the magnetic transmitter 310 and is rigidly attached tothe bony structure 114. The magnetic sensor 312 includes an anchor 314for attaching the magnetic sensor 312 to the bony structure 114. It isenvisioned that the term anchor 314 encompasses pins, screws, nails, orany other attachment device known to those in the art. In someembodiments, a plurality of magnetic sensors 312 are provided that workwith the magnetic transmitter 310, as may be seen in FIG. 8. Themagnetic transmitter 310 contains magnetic field generators that candetermine the position of the magnetic sensor 312, and thus the bonystructure 114, in relation to the sensor 108. By concatenating thepositional data from the magnetic tracker 300 and the positional datafrom the sensor 108, the global position and global change in positionof the bony structure 114 may be calculated and displayed.

In a preferred embodiment, the anchor 314 is introduced in a one stepprocess transcutaneously through a sleeve 316 with an integratedimpaction device 320, as seen in FIG. 9 or as those taught in U.S. Pat.No. 5,665,092, which is hereinafter incorporated by reference. Forintra-operative access, the sleeve 316 can be affixed to the anchor 314in order to create an access tunnel that will not interfere with thesurrounding tissue. In addition, or alternatively, a retrieval device322 is connected to the sensor 108. The retrieval device 322 maycomprise a guide wire or guide fiber to facilitate penetration throughthe tissue of the body 112 and/or for extraction of the magnetic sensor312 after the user is finished. In some embodiments, the retrievaldevice 322 is attached to the first side 180 where the magnetic tracker300 is disposed.

FIG. 10 shows yet another embodiment, wherein the positional device 110is a fiber optic device 400. Fiber optic devices, such as those found inU.S. Pat. No. 5,633,494 and U.S. Pat. No. 6,127,672, are well known inthe art and are herein incorporated by reference. Any of the priorembodiments pertaining to the surgical navigation system 104, thesubstrate 106, the sensor 108, or any other structure utilized with theultrasonic imaging device 200 and the magnetic tracker 300 may be usedin the present embodiments.

The fiber optic device 400 is disposed on the first side 180 of thesubstrate 106, while the sensor 108 is disposed on the second side 182.The fiber optic device 400 includes a non-rigid tubular attachment 402of known length that has at least one fiber 404. In a preferredembodiment, the fiber 404 is a light conducting fiber commonly known asa fiber optic wire. The tubular attachment 402 extends from the fiberoptic device 400 to the anchor 314 that can be removably attached to thebony structure 114. The tubular attachment 402 may also act as apenetration device for guiding the anchor 314 through the tissue of thebody 112 and as a retrieval device for aiding in extracting the anchor314 after the user is finished. Any of the structure or methods used toattach and remove the anchors 314 in the embodiments utilizing themagnetic trackers 300 may also be used in the present embodiments.Bending of the fiber 404 within the tubular attachment 402 correspondsto the position of the anchor 314. The fiber optic device 400 can usethe positional data of the anchor 314 to relay where the bony structure114 is in relation to the sensor 108.

FIG. 11 illustrates a cross sectional view of the fiber 404. The fiber404 usually includes a cladding 406 surrounding the length of the fiber404. In the present embodiment, a bending sensor 408 is created byremoving the cladding 406 from around a portion of the fiber 404 and/orserrating the underlying portion. In one embodiment depicted in FIG. 12,the bending sensor 408 may be treated with a light absorbent material410 to prevent light from being reflected back into the bending sensor408. The light absorbent material may serve other purposes as well, suchas protecting the fiber against environmental contamination. One skilledin the art will know how to create the bending sensor 408 and whatmaterials to use for the light absorbent material 410.

The fiber optic device 400 utilizes photo detectors to determine theamount of light lost over the serrated portion comprising the bendingsensor 408. The modulation in intensity of the light traveling throughthe fiber 404 is linear with the curvature of the fiber 404. Therefore,the amount of light lost through the bending sensor 408 is a function ofthe position of the anchor 314. FIG. 13 depicts a fiber 404 with abending sensor 408 located on a side of the fiber 404. A vertical plane412 transmits the greatest amount of light when bent. If the fiber 412is bent concave upward along the vertical plane 412, the transmissionincreases. If the fiber 404 is bent concave downward, the transmissiondecreases. A horizontal plane 414 corresponds with the least amount oflight being lost when bent along this plane 414. Intermediate responsesoccur on planes not lying within the aforementioned two planes, such asa plane 416.

One embodiment of the present invention allows the fiber 404 to extendfrom the portion of the fiber optic device 400 disposed on the firstside 180 of the substrate 106 to the anchor 314 that is removablyattached to the bony structure 114 and back to the fiber optic device400. The single fiber 404 includes one bending sensor 408 disposed at anend of a loop formed by the fiber 404 between the photo detectors andthe end of the loop disposed on the anchor 314. In an alternativeembodiment depicted in FIG. 14, the loop of fiber 404 formed near theanchor 314 is eliminated by first and second fibers 418, 420,respectively. Light from a sending photo detector 422 is sent through abending sensor 408 to a first end 424 of the first fiber 418. The firstend 424 includes a first sensing portion 426 that faces a second sensingportion 428 at the second end 430 of the second fiber 420. The twosensing portions 426, 428 include non-cladded and/or serrated portionsto allow for light transfer. Light from the second fiber 420 is thentransmitted to a retrieving photo detector 432. A cap 434 or othercovering mechanism covers the sensing portions 426, 428 and holds themin a rigid fashion so that they do not bend. The cap 434 may be disposedadjacent or within the anchor 314. This arrangement allows the first andsecond fibers 418, 420 that run parallel to each other to perform thesame function without a looped end. An added advantage is that such anarrangement allows for the bending sensors 408 to be placed in morenarrow structures, which is particularly advantageous for surgicalprocedures that want to minimize the invasiveness of the procedure. Oneskilled in the art will realize there are numerous ways to utilizelooped or non-looped fibers to convey bending, particularly in themanner in which light is transmitted from the first fiber 418 to thesecond fiber 420 in non-looped systems.

In other embodiments of the present invention multiple fibers 404 may beused as opposed to the one or two discussed above. FIG. 15 shows apreferred embodiment wherein three fibers 436 a, 436 b, 436 c are placedparallel to each other. Each fiber 404 has a bending sensor 408 thatwill relay different bending vector components. The bending sensors 408are arranged to allow for the axes of maximum light transmission to be120 degrees from each other. The three fibers 436 a, 436 b, 436 c arecorrespondingly coupled with three other fibers (not shown) in a similararrangement as seen in FIG. 14. The three fibers 436 a, 436 b, 436 ceach have an end that corresponds with respective ends of the otherthree fibers. This embodiment allows for a relatively narrow structureto be used while also receiving three bending vector components. Thethree bending vector components are beneficial in calculating a moreaccurate positioning of the anchor 314 as opposed to single or two fibersystems. It is envisioned that a plurality of different numbers andarrangements of fibers 404 may be used in different embodiments.

The number of bending sensors 408 provided within the tubular attachment402 may also vary. FIG. 16 shows a series of bending sensors comprisinglooped fibers disposed within the tubular attachment mechanism. Byproviding a series of looped sensors 440, numerous positionaldeterminations may be taken that can be combined to realize a moreaccurate position of the anchor 314 relative to the sensor 108. Oneskilled in the art will realize that numerous combinations and types offiber arrangements exist that provide for multiple bending sensors 408along the length of a material.

In all embodiments utilizing the fiber optic device 400, data isreceived by the fiber optic device 400 corresponding to the position ofthe anchor 314 attached to the bony structure 114. As mentioned before,there is also a known relationship between the sensor 108 and the fiberoptic device 400 on the substrate 106. Data corresponding to theposition of the bony structure 114 relative to the sensor 108 is relayedby the fiber optic device 400 in a manner similar to the otherembodiments discussed above.

INDUSTRIAL APPLICABILITY

The systems and methods disclosed herein assists in determining aposition and relative movement of an anatomical structure within apatient.

Numerous modifications to the present invention will be apparent tothose skilled in the art in view of the foregoing description.Accordingly, this description is to be construed as illustrative onlyand is presented for the purpose of enabling those skilled in the art tomake and use the invention and to teach the best mode of carrying outsame. The exclusive rights to all modifications which come within thescope of the appended claims are reserved.

We claim:
 1. A system for determining a position and a change in theposition of an anatomical structure, comprising: a surgical navigationsystem; a substrate comprising means for removably and non-invasivelyattaching the substrate to an outer surface of a body, wherein the bodyincludes an anatomical structure; a sensor attached to the substratethat can be tracked by the surgical navigation system to determine aposition of the sensor; an ultrasonic imaging device attached to thesubstrate and utilized to determine a position of the anatomicalstructure relative to the sensor; a first circuit for calculating aglobal position of the anatomical structure by concatenating theposition of the sensor and the position of the anatomical structurerelative to the sensor; a second circuit for displaying the globalposition of the anatomical structure on a display unit; and a pointsource adapted to be disposed adjacent the anatomical structure, whereinthe ultrasonic imaging device and the point source are utilized todetermine the position of the anatomical structure relative to thesensor, wherein the ultrasonic imaging device comprises a plurality ofultrasound transducers and the point source is a passive point sourcethat comprises a plurality of sonic reflective balls adapted to bedisposed adjacent the anatomical structure, and wherein the ultrasoundtransducers are controlled so as to emit an ultrasonic beam one at atime, wherein each ultrasonic beam reflected by at least one of thesonic reflective balls to the ultrasound transducers is received by eachof the ultrasound transducers to determine the position of theanatomical structure relative to the sensor.
 2. The system of claim 1,wherein each of the plurality of sonic reflective balls aresubstantially composed of air.
 3. The system of claim 1, wherein each ofthe plurality of sonic reflective balls comprise a resorbable material.4. The system of claim 1, wherein the anatomical structure is a bonystructure, the sensor comprises an optical tracking device, and thesubstrate is approximately 5 cm in width and approximately 5 cm inlength.
 5. The system of claim 1, wherein the means for removably andnon-invasively attaching the substrate to an outer surface of a bodycomprises an adhesive.
 6. The system of claim 1, wherein the means forremovably and non-invasively attaching the substrate to an outer surfaceof a body comprises a band.
 7. A system for determining a position and achange in the position of an anatomical structure, comprising: asurgical navigation system; a substrate comprising means for removablyand non-invasively attaching the substrate to an outer surface of abody, wherein the body includes an anatomical structure; a sensorattached to the substrate that can be tracked by the surgical navigationsystem to determine a position of the sensor; an ultrasonic imagingdevice attached to the substrate and utilized to determine a position ofthe anatomical structure relative to the sensor; a first circuit forcalculating a global position of the anatomical structure byconcatenating the position of the sensor and the position of theanatomical structure relative to the sensor; a second circuit fordisplaying the global position of the anatomical structure on a displayunit; and a point source adapted to be disposed adjacent the anatomicalstructure, wherein the ultrasonic imaging device and the point sourceare utilized to determine the position of the anatomical structurerelative to the sensor, wherein the ultrasonic imaging device comprisesa plurality of receivers and the point source is an active point sourcethat comprises a plurality of source transducers adapted to be disposedadjacent the anatomical structure, and wherein the source transducersare controlled so as to emit an ultrasonic beam one at a time, whereineach ultrasonic beam is received by each of the receivers to determinethe position of the anatomical structure relative to the sensor.
 8. Thesystem of claim 7, wherein the anatomical structure is a bony structure,the sensor comprises an optical tracking device, and the substrate isapproximately 5 cm in width and approximately 5 cm in length.
 9. Thesystem of claim 7, wherein the means for removably and non-invasivelyattaching the substrate to an outer surface of a body comprises anadhesive.
 10. The system of claim 7, wherein the means for removably andnon-invasively attaching the substrate to an outer surface of a bodycomprises a band.